1. Field of the Invention
The present invention generally relates to an ignition control apparatus for an internal combustion engine installed on a motor vehicle such as a two-wheeled vehicle, a buggy car or the like. More particularly, the present invention is concerned with the ignition control apparatus for the internal combustion engine which apparatus is capable of automatically inhibiting ignition control upon occurrence of reverse rotation of the internal combustion engine operating in a low rotation speed range and which apparatus can be implemented inexpensively without incurring any appreciable increase of manufacturing cost.
2. Description of Related Art
In the conventional ignition control apparatus for the internal combustion engine known heretofore, a rotor driven rotationally by the internal combustion engine and having a projection formed on the outer periphery is employed in combination with a rotation sensor disposed in opposition to the projection of the rotor, wherein the rotation sensor is designed to generate a crank angle detection signal in the form of a pulse signal which includes a falling voltage waveform signal of negative (minus) polarity corresponding to a leading-edge portion of the projection of the rotor as viewed in the rotating direction thereof and a rising voltage waveform signal of positive (plus) polarity which corresponds to a trailing edge portion of the projection.
In general, the leading edge portion of the projection of the rotor is set at a crank angle reference position for a timer ignition control in an ordinary operation mode of the internal combustion engine, while the trailing edge portion of the projection is set at a crank angle reference position which corresponds to a fixed ignition timing for a retard ignition control in an operation range of low rotation speed.
The ignition control apparatus is designed to carry out the ignition control at the time point (timing) when the rising voltage waveform signal of positive polarity (corresponding to the trailing edge portion of the projection of the rotor) is generated in order to suppress or prevent variance of the ignition timing in the engine operation range of low rotation speed such as in the starting operation, idling operation or the like.
In addition, the ignition control apparatus is designed to detect the rotation speed of the engine on the basis of the inter-pulse period every time the falling voltage waveform signal of negative polarity (corresponding to the leading edge portion of the projection) is generated in order to control the ignition timing by setting a predicted ignition timing for the timer control with reference to the generation timing of the falling voltage waveform signal of negative polarity in the ordinary operation mode (engine operation in a high rotation speed range).
However, when the operation of the internal combustion engine is started or stopped, there may arise such situation that the crank shaft can not pass over the compression stroke, as a result of which reversal of the engine rotation takes place. In that case, the ignition control may unwantedly be carried out although it depends on the status of the rising voltage waveform signal of the rotation sensor, whereby the reverse rotation of the engine is promoted, giving rise to a serious problem.
The reason why the ignition control is performed when the engine rotation is reversed can be explained by the fact that when the rotation reversal takes place at a time point the rotation sensor is positioned, for example, in the vicinity of a mid portion of the projection, the leading edge portion of the projection of the rotor is detected again by the rotation sensor due to the reverse rotation, whereby the leading edge portion of the rotor projection is erroneously recognized as the trailing edge portion of the rotor projection. Furthermore, in this case, the rotor projection tends to move away from the rotation sensor (i.e., the gap between the projection and the rotation sensor tends to spread). Consequently, the rotation sensor signal assumes the same polarity as that of the rotation sensor signal generated in response to the trailing edge portion of the projection in the forward engine rotation mode. For this reason, recognition or detection of the reverse rotation of the engine is rendered impossible.
When the ignition control is executed upon reversal of the engine rotation, there may arise such situation that the reverse rotation of the engine is promoted or accelerated, bringing about a so-called kicking or kick-back phenomenon or event (i.e., reverse torque transmission to the starter apparatus), whereby a starter apparatus may unwantedly be damaged.
For coping with the problems mentioned above, it has already been proposed that a rotor of a magneto-generator is used in combination with the rotation sensor to detect a coil signal induced by magnets incorporated in the rotor in addition to the rotation sensor signal for detecting the forward or reverse rotation of the engine on the basis of the phases of the coil signal and the rotation sensor signal, respectively, to thereby validate the ignition signal in the forward rotation mode of the engine while invalidating the ignition signal in the reverse rotation mode (i.e., when the internal combustion engine rotates in the reverse or backward direction).
Furthermore, such an ignition control apparatus has also been proposed that the forward/reverse rotation state is discriminatively decided by detecting the phase of the rotation sensor signal generated when the rotation sensor traverses a plurality of projections disposed on the rotor and the phase of the coil signal of the magneto-generator in combination. For more particulars, reference may have to be made to Japanese Patent No. 3142436.
In that case, the retard ignition control for the low speed engine rotation in the starting operating mode is performed at the fixed ignition position without using the predicted ignition timing.
In the conventional ignition control apparatus for the internal combustion engine, the coil signal is detected by making use of the rotor of the magneto-generator for discriminatively determining or identifying the reverse rotation state, for which a coil signal detecting circuit is required in addition to the detection circuit for the rotation sensor signal, giving rise to a problem that the manufacturing cost is increased correspondingly. Besides, because a part of the electric power generated by the magneto-generator is consumed for the detection of the coil signal, the rated capacity intrinsic to the magneto-generator is thereby degraded, giving rise to an additional problem.